Double sided printed security document

ABSTRACT

The invention concerns a security document comprising, as security element against recto/verso copying, indicia present on both sides and capable of being viewed under reflected lighting and forming an image capable of being viewed under transmitted light. The invention is characterized in that said indicia comprise lines and form said image with 3D effect.

The invention relates to a security document that includes, as copyprotection element, printed lines on both sides of the document that canbe observed in reflected light and form an image that can be observed intransmitted light.

To combat the counterfeiting of banknotes by two-sided photocopying orusing a scanner and a printer, patterns on the front side and patternson the reverse side of the banknote have been produced, by suitableregistration in a given region, so that these patterns combine to form afinal image or representation, for example a set of graphical lines oralphanumeric characters or an image of a person or animal, etc. When thebanknote is viewed in reflected light, only the pattern produced on theobserved face is seen whereas, when the banknote is observed intransmitted light, all the patterns that therefore combine to give thefinal representation are seen. According to a variant of these printedindicia, identical patterns are produced on the front side and on thereverse side by superposing them so as to observe, in transmitted light,an image that is also identical to the patterns. These patterns areproduced by printing areas of flat tint or by printing lines. A personskilled in the art refers to these as “see-through” indicia or, in thecase of the variant, as “print-through” indicia. Certain banknotes havea weight and an opacity that are sufficiently low to allow thesepatterns to be observed provided that the printed indicia are flat tintsand/or not too fine.

To be able to apply these indicia to security documents having a higherweight and/or higher opacity, it has been proposed, in European patentapplication EP 388 090, to print these indicia in a region of reducedopacity, this region being produced specifically by a watermark obtainedin a conventional manner. European patent application EP 687 324proposes a region of reduced thickness and reduced opacity with an areaof more than 0.4 cm² by providing a two-ply paper, one ply of which hasa region of reduced or even zero thickness.

Moreover, the means for reproducing the patterns, such as photocopiersand scanners, allow two-sided color copying and have the capability ofever finer resolution; it is therefore endeavored to produce patternsthat are more difficult to counterfeit.

However, the Applicant has found that, at the present time, indicia madefrom flat tints are the most widely used but also are relatively easy toproduce by two-sided color photocopiers or scanners. For example,current banknotes of the new European Community currency, namely euros,have, in one of their corners, on both sides of the banknote, printedareas of flat tint with the dominant color of said banknote whichindicate the value of the banknote, observable when it is held up to thelight. These euro banknotes do not have a region of reduced opacity andthe areas of flat tint are quite coarse and could be quite easy toreproduce.

As regards the printing of lines, the abovementioned, European patentapplication EP 388 090 has described the printing of concentric circlespresent alternately on the front side and on the reverse side of asheet, but these circles do not have any particularity and could bequite easily counterfeited by current reproduction means.

The objective of the Applicant is to provide a security document havingan enhanced level of security against two-sided copying.

The Applicant proposes to achieve this objective by providing a securitydocument that includes, as security element against two-sided copying,printed indicia present on the front side and on the reverse side thatare observable in reflected light and form an image that can be observedin transmitted light, said printed indicia comprising lines and formingsaid image such that it has a relief and volume effect, i.e. athree-dimensional or 3D effect.

Preferably, the final image that can be observed in transmitted lighthas a 3D effect obtained by variations in density expressed as numberper unit area, and/or variations in printing intensity of the lines. Theexpression “variations in density expressed as number per unit area”should be understood to mean that the distances between the lines arevaried.

Preferably, the lines are present in large number and are very fine.

According to one particular embodiment of the invention, the lines aremade from broken lines, in particular discrete dots, i.e. separate dots.

One particular way of producing the lines may be to print the lines suchthat two adjacent lines of the image are always such that one of thelines is on one side and the next line on the other side.

More generally, another approach may be to print, by means ofalgorithms, series of lines on one side and their complements on theother. They may be parallel or may intersect. All the lines on the frontside and the reverse side may be determined by mathematical means,encryption, etc.

According to a variant of the invention, the printed lines on the frontside and on the reverse side are identical and superposed.

The image to be observed when held up to the light may be an image assuch, but also part of a larger image or portrait, and in particular onealready existing on the document.

More particularly, the lines are black lines and/or in various shades ofgray and/or in color and/or they change appearance depending on theviewing angle or under the action of an excitation source, such asradiation, especially fluorescent, thermochromic or photochromic ones,and/or have electromagnetic properties, especially electricallyconducting, magnetic or magnetic resonance properties.

The document may also include printed areas of flat tint. Of course, thesecurity document may include other security elements, especially asecurity thread, flakes, iridescent printing, etc.

More particularly, the invention relates to a banknote.

Preferably, the printed indicia are produced in a region of reducedopacity.

In the case of a paper, this region of reduced opacity may be a regionsuch as that described in patent application EP 687 324, i.e. a regionof reduced thickness and reduced opacity with an area of more than 0.4cm² obtained in a two-ply paper, one ply of which has a region ofreduced or even zero thickness.

According to one particular embodiment of the invention, the document istherefore a sheet of two-ply paper, one ply of which includes a regionof reduced or even zero thickness and has an area of more than 0.4 cm²,this said region having the printed indicia.

According to one particular embodiment of the invention, the documentmay have, as backing, a plastic sheet or film whose opacity allows theprinted indicia to be observed, as in the case of a paper.

Illustrative examples of a security document according to the inventionwill now be described.

According to a first example, the portrait of a man with a beard,limited to the central part of his face, i.e. his mouth, nose and partof the beard, is produced on a paper. Such an image is formed fromlines, the number density of which is varied by varying their spacing; aset of lines is printed on the front side and the complementary set onthe reverse side so as to constitute the portrait, which can be seenwhen held up to the light. The 3D, relief and volume, effect istherefore obtained by the variations in the number density of the lines.

These lines are printed by means of an offset printing machine used toprint banknotes and documents of value. These machines can print bothsides of a paper that are perfectly in registration with one another,something that an office photocopier or printer (after scanning) canachieve only with limited accuracy. The front side/reverse side printingregistration of the portrait makes it possible to achieve a clear,high-quality image that can be observed when held up to the light.

If a counterfeiter attempts two-sided photocopying of this image, hewill be unable to bring both sides of the photocopy to accurateregistration and therefore the image will no longer be clear—there willthen be a mass of lines and the image will no longer be visible when thedocument is held up to the light. Any unskilled person can thus easilyand immediately see that the document or the banknote is counterfeit.

According to a preferred embodiment of this example, this image isproduced in a region of reduced opacity. Such a region is produced, forexample, like that described in patent EP 687 324.

According to a second example, a sheet of paper is printed with a gridon one side of the sheet and the same grid in correspondence on thereverse side. Since the printing on both sides is in extremely preciseregistration on machines dedicated to the printing of banknotes andsecurity documents, and since the front side and reverse side grids arein superposition, the image of a single grid with a 3D effect appearswhen the sheet is observed held up to the light and also when observedin reflected light.

If a counterfeiter were to reproduce these grids by means of a copier orprinter (after scanning), there would be a shift of a bar or part of thebars and therefore the grid resulting from the superposition of the twogrids on the front side and reverse side would become a clump or even ablack square, although when observed in reflected light a grid would beseen on the front side or on the reverse side. Any unskilled person maythus easily and immediately see that the document or banknote iscounterfeit.

1. A security document comprising a security element against two-sidedcopying, said security element comprising: printed indicia present onthe front side and on the reverse side, wherein said printed indiciacomprise a first set of lines printed on the front side and a second setof lines printed on the reverse side, said first set of lines and saidsecond set of lines being in accurate registration with each other,wherein the first set of lines is visible and the second set of lines isnot visible observed in reflected light from the front side, and thesecond set of lines is visible and the first set of lines not visibleobserved in reflected light from the reverse side, wherein both thefirst set of lines and the second set of lines are visible observed intransmitted light from any of the front side and the reverse side, thefirst and second sets of lines being arranged to form an image observedin transmitted light, wherein the image includes a 3D effect that is arelief or volume effect created by the planar arrangement of the firstand second sets of lines observed in accurate registration intransmitted light, whereas the 3D effect would not be present if thefirst and second sets of lines were not in accurate registration,wherein the first set of lines and the second set of lines complementeach other to constitute the image so that the image with a 3D effect isvisible observed in transmitted light but not visible observed inreflected light, so as to identify an authentic security document by theaccurate registration.
 2. The security document as claimed in claim 1,wherein the 3D effect is created as a result of the lines being of (i)variable number density per unit of area, (ii) variable printingintensity, or (iii) both variable number density per unit of area andvariable printing intensity.
 3. The security document as claimed inclaim 1, wherein the printed indicia consist entirely of such lines. 4.The security document as claimed in claim 1, wherein, the lines of theimage are printed such that two adjacent lines of the image are alwayssuch that one of the lines is on one side and the next line is on thereverse side.
 5. The security document as claimed in claim 1, whereinthe lines are represented in series, one series of lines being on thefront side and its complementary series on the reverse side.
 6. Thedocument as claimed in claim 1, wherein the lines have at least one ofthe following properties: (i) they are black, (ii) they are in variousshades of gray, (iii) they are in color, (iv) they change appearancedepending on the viewing angle or under the action of an excitationsource, (v) they have electromagnetic properties.
 7. The document asclaimed in claim 6, wherein the lines change appearance depending on theviewing angle or under the action of an excitation source which is asource of radiation.
 8. The document as claimed in claim 6, wherein thelines have electromagnetic properties, and said electromagneticproperties comprise electrically conducting, magnetic or magneticresonance properties.
 9. The document as claimed in claim 7, wherein thesource of radiation comprises a source of fluorescent, thermochromic orphotochromic radiation.
 10. The document as claimed in claim 7, whereinthe source of radiation comprises a source of fluorescent, thermochromicor photochromic radiation.
 11. The security document as claimed in claim1, which comprises, as support, a paper with a region of reduced opacityand said printed indicia are present on the front side and on thereverse side in said region of reduced opacity.
 12. The document asclaimed in claim 1, wherein the lines have at least one of the followingproperties: (i) they are black, (ii) they are in various shades of gray,(iii) they are in color, (iv) they change appearance depending on theviewing angle or under the action of an excitation source, (v) they haveelectromagnetic properties.
 13. The document as claimed in claim 12,wherein the lines change appearance depending on the viewing angle orunder the action of an excitation source which is a source of radiation.14. The document as claimed in claim 12, wherein the lines haveelectromagnetic properties, and said electromagnetic properties compriseelectrically conducting, magnetic or magnetic resonance properties.